In a conventional LSI in which MISFET (Metal Insulator Semiconductor Field Effect Transistor) elements are integrated, a SRAM is broadly used as a memory combined with a Logic circuit. In recent years, miniaturization of a LSI has proceeded in order to improve processing speed thereof or to realize an increase of memory capacity. However, as a result, there is a problem of dispersion in threshold voltage caused by fluctuation of an impurity which is introduced into a semiconductor substrate.
On the other hand, a technique is known in which a tunnel leak phenomenon is suppressed by using a high dielectric constant material as a material of a gate insulating film which is thinned in accordance with miniaturization of elements. However, in general, bond between oxygen and other elements is weak in a high dielectric constant material formed by ionic bond as compared to a material formed by covalent bonding such as SiO2 the bond is broken during the semiconductor fabrication process, and thus, oxygen defect is likely to occur in a gate insulating film. This technique, for example, is disclosed in a non-patent literary document of K. Shiraishi et al., Symp. of VLSI Tech., 2004, p. 108.